With respect to a helicopter, autorotation refers to a descending maneuver when the helicopter's engine is disengaged from the helicopter's main rotor system such that the rotor blades are driven solely by an upward flow of air through the rotor rather than being driven by engine power. Autorotation is often caused by a main rotor's engine failure, a main rotor's engine malfunction, or a loss of tail-rotor effectiveness.
Performance of a successful autorotation maneuver by a helicopter pilot may allow for a relatively safe landing of the helicopter upon the occurrence of a complete engine failure in the helicopter. Failure to perform a successful autorotation maneuver can result in catastrophic consequences. Autorotation is a labor-intensive and difficult maneuver to execute, with little margin for error. Successful helicopter autorotation maneuvers are especially challenging when a helicopter has an engine malfunction in a degraded visual environments (DVE) such that a helicopter pilot might not be able to see terrain and obstructions while trying to safely land the helicopter. Due to difficulty and safety implications related to helicopter autorotation maneuvers, helicopter pilots engage in significant and continued training related to autorotation.